1. Field of the Invention
The present invention relates to a method for automatic diagnosis of malfunctions in processes and/or installations which are monitored by sequence control from a PLC program which is produced as a contact plan (KOP), as a function plan (FUP) or as an instruction list (AWL).
2. Description of the Related Art
Manufacturing processes and manufacturing installations are controlled by programmable Logic Controllers, which are in general called PLCs, in various fields of technology. The software of such PLCs is normally produced on programming units as a contact plan (KOP), as a function plan (PUP) or as an instruction list (AWL). This is illustrated in detail, for example, in SPS-Magazin PLC Magazine! (1993), Issue 5, pages 16 to 19 and pages 39 to 40, in particular in the publication called "Einheitliche SPS-Programmierung mit IEC 1131-3" Standard PLC programming with IEC 1131-3!. The forms of program representation stated there are largely equivalent and, in particular, the contact plan (KOP) and/or function plan (FUP) can be converted into an instruction list (AWL). In addition to the stated tools for programming, the distinction is also drawn between two different program types, to be precise step chain control and logic operation control.
In the event of a defect, or malfunction in a PLC-controlled process, the cause of the defect normally has to be localized using the PLC program and the operands used in it--such as markers, data words, input/output bits--in order to take suitable measures for defect rectification. Particularly well-trained specialists are required for this purpose, who carry out fault diagnosis. German Patent Document DD-A-300 134 discloses a method for monitoring, based on rules, by diagnosis and therapy control, in particular for hierarchically structured automation systems (ATS). The status of the ATS is continuously monitored in closed-loop operation, and the truth values relating to specified diagnosis conditions are at the same time kept up to date in a diagnosis vector. Empirical knowledge relating to installation movement, which is available in the form of rules, forms the knowledge base in a specific, compressed information presentation which is evaluated on an event-controlled or time-controlled basis by means of the diagnosis vector. If an ATS condition which is worthy of therapy is indicated, the control operations which are suitable on the basis of experience are implemented automatically. Time monitoring and obviousness checking are possible at the same time.
Canadian Patent Document CA-A-21 07 051 and the corresponding European Patent Document EP-A-590 571 describe a knowledge-based method for automatic diagnosis of defects in industrial production installations. In this case, a knowledge base having a hierarchy of knowledge elements is produced which provides the operator with advice and instructions, makes it possible for him to localize the cause of a fault and provides the best-possible solution for the respective problem.